Flow Of Geomagnetically Induced Currents Research Articles

Investigating Harmonic Distortion in Power Transformers Due to Geomagnetically Induced Current Flows

Geomagnetically induced currents (GICs) flow through grounding circuits into power systems, when triggered by geomagnetic disturbances. Power transformers (with grounding connections) are the primary path for GIC flows into power systems. The flow of GICs through a power transformer can create adverse impacts on its operation, including large increases in its reactive power demands and significant harmonic distortions in the primary side currents. This paper presents case studies and analyses of the adverse impacts of GIC flows on power transformers. Presented case studies are conducted on two power transformers with different core types, power ratings, and voltage ratings. Each of these power transformers is tested for various levels of GIC flows with its loading being kept unchanged. Results of conducted case studies conclude that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2^{\text{nd}}$</tex-math></inline-formula> harmonic is the dominant in primary and side currents at all levels of GIC flows. Other harmonic components such as the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$3^{\text{rd}}$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$4^{\text{th}}$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ 5^{\text{th}},\ 6^{\text{th}},\ 7^{\text{th}}\ \text{and}\ 8^{\text{th}}$</tex-math></inline-formula> harmonic components, can be observed with lower magnitudes than the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2^{\text{nd}}$</tex-math></inline-formula> harmonic component.

The Lehtinen–Pirjola method modified for efficient modelling of geomagnetically induced currents in multiple voltage levels of a power network

Abstract. The need for accurate assessment of the geomagnetic hazard to power systems is driving a requirement to model geomagnetically induced currents (GIC) in multiple voltage levels of a power network. The Lehtinen–Pirjola method for modelling GIC is widely used but was developed when the main aim was to model GIC in only the highest voltage level of a power network. Here we present a modification to the Lehtinen–Pirjola (LP) method designed to provide an efficient method for modelling GIC in multiple voltage levels. The LP method calculates the GIC flow to ground from each node. However, with a network involving multiple voltage levels, many of the nodes are ungrounded, i.e. have infinite resistance to ground, which is numerically inconvenient. The new modified Lehtinen–Pirjola (LPm) method replaces the earthing impedance matrix [Ze] with the corresponding earthing admittance matrix [Ye] in which the ungrounded nodes have zero admittance to ground. This is combined with the network admittance matrix [Yn] to give a combined matrix ([Yn] + [Ye]), which is a sparse symmetric positive definite matrix allowing efficient techniques, such as Cholesky decomposition, to be used to provide the nodal voltages. The nodal voltages are then used to calculate the GIC in the transformer windings and the transmission lines of the power network. The LPm method with Cholesky decomposition also provides an efficient method for calculating GIC at multiple time steps. Finally, the paper shows how software for the LP method can be easily converted to the LPm method and provides examples of calculations using the LPm method.

GICharm: A System Level Analysis Tool for Geomagnetic Disturbance Related Harmonics

Power systems can and have been impacted by harmonics generated during geomagnetic disturbances (GMD) events. These harmonics are generated from the part-cycle saturation of power transformers caused by the flow of geomagnetically-induced currents through grid-connected transformers. This article describes a system level harmonic analysis tool needed by the industry to perform an adequate assessment of GMD-related distortion impacts. When the results of a properly performed harmonic assessment are combined with the fundamental frequency analyses, a much more accurate evaluation of grid security during GMD can be obtained. The tool is publicly available for engineers, students, and researchers. It provides multiple examples, including a validation against published measurements from an experimental setup consisting of two back-to-back connected transformers in the Fingrid power network. Final of this article briefly discusses the results of that validation.

New Detailed Modeling of GICs in the Spanish Power Transmission Grid

AbstractThe threat of Geomagnetically Induced Currents (GICs) driven by severe Space Weather looms over technological systems such as power grids. Assessing their vulnerability is thus vital to avoid damages or even disruption of the electrical power supply. This endeavor, however, entails an interdisciplinary approach, ranging from the characterization of the geoelectrical structure of the Earth beneath and around the area of interest, or the modeling of the power network from its parameters and topology, and including the validation of the modeling process by means of (direct or indirect) GIC flow measurements. In this paper, we summarize our current achievements focused on mainland Spain, concentrating on the improvements reached after going from a homogeneous Earth's resistivity to an alternative 3D electrical resistivity distribution approach to geoelectric field computation, which is still in progress because new empirical impedance tensors are needed, mainly at sites in the west of the Iberian Peninsula. The second major achievement has come from the addition of the 220 kV level to the network model. The overall improvement has been validated against real GIC data in one area of the country. The new vulnerability maps show that in some nodes the predicted GIC has been substantially reduced by the sum of both effects. The assessment has been carried out down to the level of the individual windings of each transformer, and examples of the estimated GIC flow are given for substations with numerous power transmission lines converging to them at diverse orientations.

Wavelet and Network Analysis of Magnetic Field Variation and Geomagnetically Induced Currents During Large Storms

AbstractDuring geomagnetic storms rapid magnetic variations cause large, sharp enhancements of the magnetic and geoelectric field at mid‐latitudes. These present a potential hazard to grounded technology such as high voltage transformers, pipelines and railway systems. Spatiotemporal quantification can provide insight into the magnitude and configuration of their potential hazard. We use the Haar wavelet transform to localize in time and frequency the storm‐time response in both European ground‐based magnetometer measurements and modeled geomagnetically induced currents (GICs) from the high voltage grid of Great Britain (GB). Wavelet cross‐correlation of the GIC in the grounded nodes is then used to build a time‐varying network of GIC flow around the GB grid during storms including the 2003 Halloween storm. We find a highly intermittent (few tens of minutes duration) long‐range coherent response that can span the entire physical grid at most intense times. The spatial pattern of response seen in the GIC flow network does not simply follow that of the amplitude of the rate of change of B field. Coherent response is excited across spatially extended clusters comprised of a subset of nodes that are highly connected to each other, with a tendency for east‐west linkages following that of the physical grid, simultaneous with the overhead presence of the auroral electrojet and the inducing component of the magnetic field. This can quantify the spatial and temporal location of increased hazard in specific regions during large storms by including effects of both the geophysical and engineering configuration of the high voltage grid.

On the impact of geomagnetically induced currents in driving series capacitor compensated power systems to ferroresonance

Solar storms cause disturbances in the Earth's magnetic field, which results in quasi-DC geomagnetically induced currents (GICs) flow in the grounded sections of the system. The flow of GICs in the power system may drive the power transformers to the saturation region. Moreover, HV transmission lines are often compensated by series capacitor units for enhancing the capability of power transmission lines. The proximity of power transformers and series capacitor compensation units during GICs may enhance the chance of the ferroresonance phenomenon in power transformers. The occurrence of ferroresonance produces extensively high voltages/currents in system apparatus, including transformers which can consequently result in severe damages. This paper puts forward the analysis of the power transformer ferroresonance phenomenon due to GICs in series capacitor compensated networks. This issue has been addressed through mathematical analysis and verified by an experimental test setup, in order to demonstrate the effect of GIC on ferroresonance. Through the employment of an example test system in EMTP-RV environment, impacts of different involving parameters such as system loading, compensation level, and substations' grounding resistances are evaluated on the occurrence of ferroresonance due to GICs. The results indicate that for series capacitor compensated power grids, GICs can profoundly enhance the vulnerability of power transformers to the occurrence of ferroresonance phenomena.

Geomagnetic Induced Current Measurement in Hybrid PV-Wind System Transformers

Geo magnetically induced currents (GICs) can cause saturation of the magnetic core of transformers in a power system. This saturation can conduce to generating harmonic currents, voltage-control problems and overheating of the transformer internal components, leading to gas relay alarm/operation and possible damage. In this work, GICs effects have been analyzed on hybrid PV-wind system transformers. The system implemented through using Power System Computer Aided Design (PSCAD/EMTDC) platform and made up of 2.1 MW wind farm, 2 MW solar photovoltaic (PV) farm, power storage system and load. Then the system is integrated with 33 kV grids through a 480V AC bus and step-up wye/delta transformer. In addition, Pi-section has been used between different parts of the system. The GIC is modeled as a controlled DC voltage source and inserted into the system through a neutral point of a wind turbine (WT) transformer. The simulation results of reactive power, voltage and current waveforms, and non-linear behavior due to asymmetric saturation of the magnetic core in the transformer due to 100 A GIC current injections are obtained. Moreover, different GIC blocking devices have been applied to mitigate or eliminate the flow of GIC to the system.

The Influence of Geomagnetic Storms on Thermal Processes in the Tank of a Power Transformer

Modeling issues devoted to the thermal processes in the tank of five-legged core-type power transformers, when exposed to geomagnetically induced currents (GICs), were considered. The method of calculation of additional eddy current losses and temperature of the most heated point of a power transformer tank while flowing through grounded windings of GICs was developed. It was shown that recording heat-exchange processes—convection and irradiation—while GICs flow through grounded windings of the power transformer enables refining the temperature increase of the most heated point of the tank. The results of calculation of the additional losses on the coordinates on the tank walls and the temperature change rate in the most heated point of the five-legged core-type power transformer TDC-400000/242/20 tank during the heat exchange between the tank and air and oil depending on the value of GIC are presented. The dependencies of temperature increase in the most heated point of the transformers tank on the geoinduced currents of different values were calculated. The limit values of temperature increase were determined. The comparison of obtained values with their temperature limits set up in standard IEC 60076-7 are given.

Comparison of methods for modelling geomagnetically induced currents

Abstract. Assessing the geomagnetic hazard to power systems requires reliable modelling of the geomagnetically induced currents (GIC) produced in the power network. This paper compares the Nodal Admittance Matrix method with the Lehtinen–Pirjola method and shows them to be mathematically equivalent. GIC calculation using the Nodal Admittance Matrix method involves three steps: (1) using the voltage sources in the lines representing the induced geoelectric field to calculate equivalent current sources and summing these to obtain the nodal current sources, (2) performing the inversion of the admittance matrix and multiplying by the nodal current sources to obtain the nodal voltages, (3) using the nodal voltages to determine the currents in the lines and in the ground connections. In the Lehtinen–Pirjola method, steps 2 and 3 of the Nodal Admittance Matrix calculation are combined into one matrix expression. This involves inversion of a more complicated matrix but yields the currents to ground directly from the nodal current sources. To calculate GIC in multiple voltage levels of a power system, it is necessary to model the connections between voltage levels, not just the transmission lines and ground connections considered in traditional GIC modelling. Where GIC flow to ground through both the high-voltage and low-voltage windings of a transformer, they share a common path through the substation grounding resistance. This has been modelled previously by including non-zero, off-diagonal elements in the earthing impedance matrix of the Lehtinen–Pirjola method. However, this situation is more easily handled in both the Nodal Admittance Matrix method and the Lehtinen–Pirjola method by introducing a node at the neutral point.

Effects of Series Compensation Capacitors on Geomagnetically Induced Currents

A series compensation capacitor bank presents a high-impedance path to geomagnetically induced currents (GICs), which are induced into the power network during geomagnetic disturbances. The notion that a series capacitor generally blocks GIC is only true for the transmission circuit connected in series with the capacitor. In many cases, the series capacitor simply re-distributes GIC in the network and may actually increase GIC flow at terminal stations. The conditions under which an increase in GIC can take place and illustrative examples with and without piecewise layered earth modeling are discussed.

Effects of neutral point reactors and series capacitors on geomagnetically induced currents in a high‐voltage electric power transmission system

Geomagnetically induced currents (GIC) are DC‐like currents compared to power transmission frequencies. Consequently, it may be possible to reduce the magnitudes of GIC by installing resistive components or series capacitors into a power grid. We simulate the effects of neutral point reactors and series capacitors on GIC in the Finnish 400 kV network. Reactors add an additional resistance to earthing leads of transformers, and series capacitors block the flow of GIC in transmission lines. The geoelectric field impacting the system is considered to be uniform. The use of reactors does not necessarily reduce the GIC risk. Although the installation of reactors tends to decrease GIC on the average, maximum GIC may even increase. Assuming a reactor at all stations results in a 50% reduction of the maximum GIC compared to the situation with no reactors. With up to four series capacitors, the maximum GIC is reduced by 40% when they are optimally located. However, even small changes in the topology of the grid can cause large changes in GIC. A combination of reactors and series capacitors could in principle provide a way to diminish the GIC risk. This study also emphasizes the difficulty of preventing GIC problems by these means.

European Project to Improve Models of Geomagnetically Induced Currents

Geomagnetically induced currents (GICs) from solar storms pose a risk to the operation of power transmission grids in Europe and across the globe. The European Risk from Geomagnetically Induced Currents (EURISGIC) project, which began in March 2011 and is supported by the Seventh Framework Programme of the European Union, seeks to mitigate this natural hazard by developing European capabilities for GIC forecasting and warning. Recent well-recognized GIC events were the province-wide blackout in Quebec, Canada, in March 1989 and the blackout in the city of Malmö, in southern Sweden, during the Halloween storm of October 2003. The progressive integration of interconnected and geographically wide power transmission grids is obviously increasing the GIC risk. Hence, there is a need for greater scientific understanding of phenomena in the solar-terrestrial environment that lead to GICs and for the development of systems that facilitate GIC modeling, forecasting, and mitigation. Within the EURISGIC project the flow of GICs throughout the European grid for hypothetical and real events will be simulated using improved grid network models and conductivity models for the continent. The project will produce the first Europe-wide real-time prototype forecast service of GICs in high-voltage power systems, based on in situ solar wind observations by the Advanced Composition Explorer (ACE) spacecraft, empirical modeling, and comprehensive simulations of Earth's magnetosphere. Moreover, on the basis of long-term geomagnetic recordings, EURISGIC will derive the first map of the statistical risk of large GICs throughout Europe. Of special interest is a search for untapped data sources for the solar storm of September 1859, famously observed by British astronomer Richard Carrington, which is often referred to as the most intense geomagnetic storm ever recorded. The project aims to assist European scientists as they strive for 30- to 60-minute lead time forecasts of GIC events. There is presently only one European magnetohydrodynamic code for global simulations of the solar wind-magnetosphere interaction, namely, Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS-4), developed at the Finnish Meteorological Institute. During EURISGIC, GUMICS-4 will be upgraded to be able to produce real-time GIC forecasts. For this development, EURISGIC will obtain valuable contributions from the U.S. expertise gained from NASA's Solar Shield project (http://ccmc.gsfc.nasa.gov/Solar_Shield/). The U.S. and European codes will run in parallel to produce GIC forecasts in Europe, and they will also stimulate further improvements in simulations. Calculation of GICs in a given power grid is a straightforward problem, which has been considered in several previous national studies, for example, in Finland, Sweden, and the United Kingdom. The key problem is to determine the geoelectric field that drives GICs in power grids. This electric field can be calculated from the measured magnetic field using models of the Earth's conductivity. A special challenge for EURISGIC is to compile a simplified conductivity map of Europe that enables efficient computation of Europe's electric field. When the geoelectric field is known, calculation of GICs in a power grid is reduced to a simple direct current (DC) mathematical problem. In combination, early warning forecasts, risk maps, and worst-case-scenario assessments provided by EURISGIC will contribute to mitigating the risks that GICs represent, thereby avoiding destruction of transformers and enhancing the protection of critical infrastructure in Europe and elsewhere in the world. The project began in March 2011 and will last until February 2014. The Finnish Meteorological Institute is the coordinator, with Ari Viljanen as the coordinating person. Other European Union partners come from Hungary, Sweden, and the United Kingdom. In addition, Russia and the United States belong to the consortium, ensuring the best global GIC expertise within the team. An external group of advisors representing power engineering, education, and space weather services will provide independent reviewing and suggestions to help the consortium reach its ambitious goals. EURISGIC is funded by the Seventh Framework Programme of the European Union (Project 260330). The EURISGIC Web site is http://www.eurisgic.eu. The following are members of the consortium, with their representatives given in parentheses: Finnish Meteorological Institute, Finland (Ari Viljanen); British Geological Survey/Natural Environment Research Council, United Kingdom (Alan Thomson); NeuroSpace, Sweden (Magnus Wik); Swedish Institute of Space Physics, Sweden (Peter Wintoft); Geodetic and Geophysical Research Institute, Hungary (Viktor Wesztergom); Polar Geophysical Institute, Russia (Yaroslav Sakharov); and Catholic University of America, United States (Antti Pulkkinen). Ari Viljanen is a senior scientist at the Finnish Meteorological Institute, in Helsinki, Finland. E-mail: [email protected]

Geomagnetically induced currents in an electric power transmission system at low latitudes in Brazil: A case study

Geomagnetically induced currents (GICs) are a ground end manifestation of space weather processes. During large geomagnetic storms, GICs flow between the grounding points of power transformers and along electric power transmission lines connecting the transformers. In high‐latitude regions, damages to power transformers are reported where storm time geomagnetic variations are very rapid and large (&gt;1000 nT), and hence the GICs as large as or even greater than 100 A end up flowing through the windings of power transformers. At low latitudes, geomagnetic variations are less severe, and hence much smaller GIC values are generally reported there. However, the flow of GICs and their effects on power transformers are complex processes, and careful evaluation is needed even in such low‐latitude regions as, for example, Brazil. We report here a study on GIC measurements in Brazil conducted under a cooperative project between FURNAS (the Brazilian electric power company) and the National Institute for Space Research. During a large geomagnetic storm, which took place on 7–10 November 2004, the GIC amplitudes, measured on the basis of geomagnetic variations in 500 kV power transmission lines in the S–E region of Brazil, were found to be around 15 A.

The electric field in northern England and southern Scotland: implications for geomagnetically induced currents

SUMMARY Magnetotelluric (MT) data, in the form of MT tensors, are used to estimate directly the size and spatial distribution of the electric field in northern England and southern Scotland with the aim of predicting the flow of geomagnetically induced currents (GIC) in power networks in the region. MT and Geomagnetic Deep Sounding data from a number of different field campaigns, at a period of 750 s, are employed. The MT data are cast in the form of telluric vectors, which allow a joint hypothetical event analysis (HEA) of both Geomagnetic Deep Sounding and MT data. This analysis reveals qualitatively the pervasive effects of electric field distortion in the region. Two approaches are taken to understand how the spatial structure of the regional electromagnetic field is affected by local distortions, and what the origin of these distortions might be. The dimensionality, and form of electric field distortion, of the MT tensors is investigated using the Weaver et al. and Bahr classification schemes, and by examining the misfit of a galvanic distortion model as a function of rotation angle. At sites where the galvanic distortion model is found to be appropriate the regional MT tensors are recovered using tensor decomposition techniques. It is found that recovering the regional MT response reconciles the geometry of induced currents implied by the MT data with that of the Magnetic Variation anomalies. Lilley’s central impedances are used to calculate rotationally invariant effective telluric responses. In the Southern Uplands the magnitude of the effective telluric response is approximately 0.25-0.5 mV km −1 nT −1 , but as the Southern Uplands Fault is approached it rises steadily to 3 mV km −1 nT −1 . In the Midland Valley, the effective telluric response is approximately 0.5 mV km −1 nT −1 which rises steadily to 2.5 mV km −1 nT −1 as the Southern Uplands and Highland Boundary Faults are approached to the southeast and northwest, respectively. Therefore, the increase in the magnitude of the effective telluric response correlates with the approach of a major tectonic boundary such as the Southern Uplands Fault. These results show that the induced electric field strength varies considerably throughout the central Scotland region. In addition, the HEA indicates that due to lateral changes in conductivity structure the direction of the electric field deviates significantly from the regional direction implied by the polarization azimuth of the primary geomagnetic induction. Therefore, any attempts to model the flow of GIC in the region need to account for the spatial variation of both the magnitude and azimuth of the electric field.

Fundamentals about the flow of geomagnetically induced currents in a power system applicable to estimating space weather risks and designing remedies

Geomagnetically induced currents (GIC) in technological systems, like electric power transmission grids, at the Earth's surface are caused by space weather processes, whose origin is in the Sun. In power systems, transformers may be saturated due to GIC leading to different problems extending from an increase of harmonics to a blackout of the system and damage of transformers. To design reasonable measures against impending problems, GIC magnitudes in the network should be estimated in different circumstances. This paper tackles basic features of GIC flow in a fictitious five-transformer/four-line power system, which is simple enough to make the equations easily manageable but complex enough to yield real and usable information. It is shown that the direction of the geoelectric field affects GIC at different sites but the dependence is not straightforward since GIC produced in one part of the system flows to others. Generally, transmission lines experience much larger GIC than transformers. Series capacitors in transmission lines prevent the flow of dc-like GIC but, without a careful analysis, their installation may result in larger GIC at some transformers of the system thus increasing the risk of problems.

Recordings and occurrence of geomagnetically induced currents in the Finnish natural gas pipeline network

A project implemented to study the effects of space weather on the Finnish natural gas pipeline was started in August 1998. The aims of the project were (1) to derive a model for calculating geomagnetically induced currents (GIC) and pipe-to-soil (P/S) voltages in the Finnish natural gas pipeline, (2) to perform measurements of GIC and P/S voltages in the pipeline and (3) to derive statistical predictions for the occurrences of GIC and P/S voltages at different locations in the pipeline network. GIC and P/S voltage were recorded at a compressor station. The GIC measurement was made with two magnetometers, one right above the pipe, and another at the Nurmijärvi Geophysical Observatory about 30 km southwest. The largest GIC since November 1998 has been 30 A. The P/S voltage recording was stopped in May 1999, but GIC is still measured. GIC statistics were derived based on the recordings of the geomagnetic field at Nurmijärvi. The geoelectric field was calculated by using the plane wave model. This field was input to the general pipeline model resulting in the distribution of currents and P/S voltages at selected points in the pipeline. As could be expected, the largest P/S voltage variations occur at the ends of the pipeline network, while the largest GIC flow in the middle parts.

GIC mitigation: a neutral blocking/bypass device to prevent the flow of GIC in power systems

The design of a neutral blocking/bypass device which can be installed in power transformer neutral-ground connections to block the flow of geomagnetically induced currents (GICs) is described. The device consists of standard distribution capacitors which provide the GIC blocking function. The capacitors are rapidly bypassed by a combination of sparkgap and circuit breaker to solidly ground the neutral during power system disturbances. The sparkgap provides the fast operating response speed, while the circuit breaker provides a secure metallic bypass of the capacitor. Simulation indicates that the bypass device operation will occur rapidly (on the order of 1 ms or less) and will both prevent ferroresonant overvoltages and preserve proper relay and protective device operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>